The present invention is directed to electronic circuits, and, more particularly, to a tamper detection circuit for a secure module.
Tampering with a module involves unauthorized access to the module, for example with the intention of retrieving, altering or adulterating sensitive information, a product, a package, or system. A protected object may be a secured electronic module such as a payment terminal or cash dispenser for use with bank cards, an authentication terminal for use with smart cards containing identity data and other personal information, or a cryptographic module, for example. A protected object may be in an electrically secured casing, room, safe or vault, for example. Security countermeasures against tampering involve physical features making unauthorized access more difficult, including a closure such as a door, cover, casing, encapsulation or a wrapping surrounding the module. Detection of tampering typically includes detection of attack on the secured physical features.
The security of the module may include a tamper detector for detecting interference with one or more detection circuits securing access to the module. The detection circuits may be electrical conductors whose continuity is interrupted by tampering, for example conductors bridging two components or formed in a wrapping forming part of the closure and that become an open-circuit if the wrapping is pierced. Alternatively, the electrical detection circuits may have switches designed to open or close if a closure is opened. The detection circuits may alternatively include optical detection circuits and transducers. An output of the tamper detector may apply to one end of a detection circuit of the physical security feature a detection signal which the detector compares with a signal from the other end of the detection circuit received at an input of the detector in order to detect interference with the detection circuit.
More sophisticated attacks may attempts to neutralize the tamper detection. For example, an attack may include injecting a foreign signal into the detector input to simulate the detection signal and camouflage interference with the detection circuit. To complicate such an attack, the detection signal may include a pseudo-random code, that is to say a deterministic code that cannot be predicted without knowing or discovering the algorithm used to generate the code and the initial seed. Typically a linear feedback shift register (LFSR) is used to generate such a pseudo-random code. Attempts to crack a pseudo-random code may include simple and differential power analysis (SPA and DPA), which derive cryptographic intermediate values visually or by statistical analysis of variations in power consumption by the computation of the pseudo-random code.
It is desirable to avoid complications introduced into the tamper detector by tamper countermeasures for guarding against an attack that make installation and programming of the tamper detector more difficult to make and use.